1. Field of the Invention
The present invention relates to a new electric contact member used in a vacuum circuit breaker, vacuum switch or the like, a manufacturing method thereof, and a vacuum valve and vacuum circuit breaker made thereof.
2. Description of the Prior Art
The electrode in a vacuum valve installed in a vacuum circuit breaker or the like comprises a pair of electrodes on the fixed and movable sides. The electrodes on the fixed and movable sides consist of an electric contact and electrode rod connected thereto, and the back of the electric contact is often reinforced by a stainless steel plate.
Crxe2x80x94Cu composite metal is often used to manufacture the electric contact member for large current and high voltage breaking.
The electric contact is manufactured by machining an electric contact material into a specified form, wherein the electric contact material is produced in the so-called method of powder metallurgy consisting of a first step of forming metal powder of various components or a mixture thereof into a simple structure (disk form, for example) at a specified composition and a second step of sintering it. The electric contact is provided with three or more slots for giving driving force to the produced arc so that arc will move to the circumference of the electrode without allowing arc to stay at one particular point, and these slots are formed in a vane-like separate shape. The center of the electric contact is provided with a concave to ensure that arc does not occur to remain at the center of the electric contact.
The above-mentioned electric contact is exposed directly to arc since it is used to turn on or off high voltage and current. The electric contact is required to provide a high breaking capacity, high dielectric strength and high welding resistance. It is difficult to meet all these requirements. In the products offered on the market, emphasis is generally placed on especially important characteristics according to a particular application at the sacrifice of other characteristics to some extent.
A large electric conductivity is essential to ensure large breaking capacity in the Crxe2x80x94Cu composite metal, for example. This requirement can be met by the composition with an increased amount of Cu. However, this involves an decrease in the amount of Cr which increases dielectric strength, with the result that both dielectric strength and welding resistance are decreased.
Amid ever increasing amounts of voltage in power distribution business, a vacuum circuit breaker or vacuum switch is required to ensure compatibility of a large current breaking capacity with dielectric strength and welding resistance. For example, when the Crxe2x80x94Cu composite metal is used to manufacture an electric contact, dielectric strength and welding resistance can be improved by increasing the amount of Cr. Increase in the amount of Cr, however, reduces conductivity and breaking capacity, making it difficult to ensure compatibility of a large current breaking capacity with dielectric strength and welding resistance in the prior art.
Japanese patent laid-Open publication NO. 235825/2000 discloses an electrode member with fire proof metal powder having the form of a flat plate. This is produced by spray-coating of the composite metal between highly conductive metal and fire proof metal onto the contact point face. Spray coating method, however, involves spray coating gas and atmosphere, so the obtained spray coated film contains a large amount of gas. Gas is discharged by arc heating at the time of current breaking, and arc is kept there through this gas, possibly causing current breaking to be disabled. Further, the size and form of fire proof metal powder on the spayed film is difficult to control, and tend to be irregular, with the result that breaking performances are unstable. In addition, formation of sprayed film requires much time, raising problems with productivity and costs.
The object of the present invention is to provide an electric contact member characterized by excellent current breaking capacity as well as a high degree of dielectric strength and welding resistance, and the method for manufacturing this electric contact member at a low production cost with high productivity.
In an effort to attain the above object, the inventors of the present application have invented a material texture which allows a large area to be occupied by the dielectric strength component on the contact point face where current breaking is performed. Namely, in the case of Crxe2x80x94Cu electric contact, Cr particles are formed in a flat plate and the flat surfaces of Cr particles are oriented to be parallel to the contact point face in the Cu matrix. This structure allows many Cr particles to be exposed on the contact point face while reducing the amount of Cr and maintaining high conductivity, whereby high dielectric strength can be ensured. Further, the strength of the Cr particles perpendicular to the flat surface is reduced because of weak chemical bond between Cr particles and Cu matrix, and welding resistance is improved.
The following describes the summary of the present invention:
The electric contact member according to the present invention has a texture wherein fire proof metal powder having the form of a flat plate is diffused in the matrix comprising a highly conductive metal, and the electric contact member further characterized in that the flat surface of the fire proof metal powder is oriented in one direction and the surface in parallel with the flat surface of the fire proof metal powder is used as a contact point face.
The fire proof metal powder having the form of a flat plate according to the present invention is characterized in that the maximum length of the flat surface divided by the minimum dimension of the surface perpendicular thereto is within the range from 3 to 30.
The electric contact member according to the present invention is characterized in that 90 wt % or more of the fire proof metal powder having the form of a flat plate has the flat surface oriented with respect to the contact point face within the range from +40 to xe2x88x9240 degrees, and 75 wt % or more has the flat surface oriented with respect to the contact point face within the range from +20 to xe2x88x9220 degrees.
The above-mentioned fire proof metal powder according to the present invention comprises one of Cr, W, Mo, Ta, Nb, Be, Hf, Ir, Pt, Zr, Ti, Te, Si, Rh and Ru, a mixture comprising two or more of them or a compound thereof, and highly conductive metal comprises Cu, Ag, Au or an alloy mainly consisting of them.
The above-mentioned fire proof metal powder contains 50 to 2000 ppm of oxygen, 50 to 3000 ppm of aluminum and 100 to 2500 ppm of silicon.
The electric contact member according to the present invention comprises 15 to 40 wt % of the above-mentioned fire proof metal powder and 60 to 85 wt % of the conductive metal.
The electric contact member according to the present invention is characterized in that the percentage of the area occupied by the above-mentioned fire proof metal powder is 30 to 50% on the contact point face, and the percentage of the area occupied by the fire proof metal powder is 14 to 25% on the surface perpendicular to the contact point face.
The electric contact member according to the present invention contains 2500 ppm or less of oxygen, wherein the tensile strength in the direction perpendicular to the contact point face is 150 MPa or less, and the specific resistance is 5.5 xcexcxcexa9.cm or less.
The method for manufacturing an electric contact member according to the present invention characterized in that
a powder mixture consisting of the above-mentioned fire proof metal powder and highly conductive metal powder is pressure-molded at a pressure of 120 to 500 MPa to create a molded product;
this molded product is sintered under vacuum or in inert atmosphere at the melting point equal to or less than that of said highly conductive metal powder; and
a contact point face is created in parallel to the pressurized surface in the molding process.
The method for manufacturing an electric contact member according to the present invention characterized in that the obtained electric contact member is made compact by a pressure of 400 MPa or more applied in the same direction as that of the molding process.
The method for manufacturing an electric contact member according to the present invention is characterized in that
a continuous plate- or rod-formed molded product is created by extrusion and compression molding of a powder mixture consisting of fire proof metal powder and highly conductive metal powder;
the molded product is sintered continuously under vacuum or in inert atmosphere at the melting point equal to or less than that of the highly conductive metal powder; and
the surface parallel to the direction of extrusion is used as a contact point face.
The method for manufacturing an electric contact member according to the present invention is characterized in that
the obtained electric contact member is further rolled, and the contact point face is created in parallel with the rolled surface;
wherein above-mentioned rolling is performed at the normal temperature or at the melting point equal to or less than that of the highly conductive metal.
The method for manufacturing an electric contact member according to the present invention is characterized in that a desired form is obtained by punching perpendicularly to the direction of extrusion.
The method for manufacturing an electric contact member according to the present invention is characterized in that the particle size of highly conductive metal powder does not exceed 80 xcexcm.
The electric contact member according to the present invention is used as a member constituting a pair of electrodes on the fixed and movable sides
in the vacuum valve, and this vacuum valve is used in the vacuum circuit breaker, vacuum switch and the like.
The vacuum valve according to the present invention is characterized in that the value y obtained by multiplying the rated voltage (kV) by breaking current effective value (kA) is within the range from the value obtained by the following equation (1) or less to the value obtained by the following equation (2) or more, based on the outer diameter x (mm) of the vacuum container:
y=11.25xxe2x88x92525xe2x80x83xe2x80x83(1) 
y=5.35xxe2x88x92242xe2x80x83xe2x80x83(2) 
The electric contact according to the present invention is characterized in that the diameter y (mm) is within the range from the value obtained by the following equation (3) or less to the value obtained by the following equation (4) or more, based on the value x (kVAxc3x97103) obtained by multiplying the rated voltage (kV) by breaking current effective value (kA):
y=0.15x+22xe2x80x83xe2x80x83(3) 
y=0.077x+20xe2x80x83xe2x80x83(4) 
The vacuum valve according to the present invention is characterized in that the diameter y (mm) of the vacuum container is within the range from the value obtained by the following equation (5) or less to the value obtained by the following equation (6) or more, based on the diameter x (mm) of the electric contact:
y=1.26x+30xe2x80x83xe2x80x83(5) 
y=1.26x+10xe2x80x83xe2x80x83(6) 
The texture of the electric contact member according to the present invention is characterized in that fire proof metal powder having the form of a flat plate is diffused in the matrix comprising a highly conductive metal, and the flat surface of said fire proof metal powder is oriented in one direction. When this electric contact member is used as an electrode, it is preferred that the surface in parallel with the flat surface of the fire proof metal powder be used as a contact point face. This structure allows many fire proof metal particles to be exposed on the contact point face while maintaining high conductivity without increasing the amount of contained fire proof metal whereby high dielectric strength can be ensured. Further, the strength in the direction perpendicular to the contact point face is small because of weak chemical bond between fire proof metal particles and highly conductive metal matrix. This makes it easy to separate and open the contact when the electrode is welded by arc heating, with the result that welding resistance is improved.
The above-mentioned fire proof metal powder having the form of a flat plate is preferred to be characterized in that the maximum length of the flat surface divided by the minimum dimension of the surface perpendicular thereto is within the range from 3 to 30. It ensures compatibility of large current breaking capacity with dielectric strength and welding resistance if 90 wt % or more of the fire proof metal powder contained in the electric contact member has the flat surface oriented with respect to the contact point face within the range from +40 to xe2x88x9240 degrees, and 75 wt % or more has the flat surface oriented with respect to the contact point face within the range from +20 to xe2x88x9220 degrees.
The fire proof metal powder constituting the electric contact material is preferred to comprise one of Cr, W, Mo, Ta, Nb, Be, Hf, Ir, Pt, Zr, Ti, Te, Si, Rh and Ru, a mixture comprising two or more of them or a compound thereof, and highly conductive metal is preferred to comprise Cu, Ag, Au or an alloy mainly consisting of them. An electric contact member featuring excellent current breaking capacity, a high degree of dielectric strength and sound material texture can be provided if the blending ratio between fire proof metal powder and highly conductive metal is such that 15 to 40 wt % of fire proof metal powder and 60 to 85 wt % of highly conductive metal are contained.
The fire proof metal powder is preferred to contain 50 to 2000 ppm of oxygen, 50 to 3000 ppm of aluminum and 100 to 2500 ppm of silicon. This provides an excellent arc extinguishing effect at the time of breaking, thereby improving the breaking performance. Aluminum and silicon can each occur as oxides, and excellent welding resistance and dielectric strength are ensured by uniform distribution of hard and fine aluminum and silicon oxides having a high melting point.
If the amounts of aluminum and silicon are smaller than the above, the amounts of generated aluminum and silicon will be smaller, giving a little effect in improving the performance. If the amounts are greater, much gas will be produced when oxides are decomposed by arc heating at the time of breaking, thereby reducing the high dielectric strength and breaking performance.
In the electric contact member according to the present invention, the percentage of the area occupied by the above-mentioned fire proof metal powder is preferred to be 30 to 50% on the contact point face, and 14 to 25% on the surface perpendicular to the contact point face. This provides high dielectric strength and welding resistance while maintaining high conductivity.
When oxygen contained in the electric contact member is kept at 2500 ppm or less, gas discharge is reduced at the time of current breaking, and possible failure of current breaking due to arc production sustained by gas can be prevented.
When the tensile strength in the direction perpendicular to the contact point face is 150 MPa or less, and the tensile strength in the direction parallel to the contact point face is 150 MPa or more, it is easier to separate and open the contact when the electrode is welded by arc heating at the time of current breaking, with the result that welding resistance is improved.
The specific resistance of the electric contact member is preferred to be 5.5 xcexcxcexa9.cm or less. There is no anisotropy since electric characteristics depend on the amount of the highly conductive metal contained. This specific resistance ensures excellent breaking performances.
In the production of an electric contact member, it is preferred that a powder mixture consisting of fire proof metal powder and highly conductive metal powder be pressure-molded at a pressure of 120 to 500 MPa to create a molded product; and this molded product be sintered under vacuum or in inert atmosphere at the melting point equal to or less than that of the highly conductive metal powder. If the molding pressure is smaller than 120 MPa, molding density will be smaller and the molded product will be susceptible to damage. If it is greater than 500 MPa, the service life of the die and productivity are reduced. When the molded product is sintered under vacuum or in inert atmosphere, sound sintered structure and adequate amount of contained gas are ensured. The fire proof metal powder having the form of a flat plate tends to be oriented parallel to the pressurized surface in the molding process, it is preferred that the surface parallel to the pressurized surface be used as the flat surface. This ensures the characteristics intended in the present invention.
Further, the produced electric contact member is made compact by a pressure of 400 MPa or more applied in the same direction as that of the molding process. This will lead to the stability of the electrode performance, and will also reinforce the orientation of fire proof metal powder having the form of a flat plate, with the result that the characteristics intended in the present invention are improved.
In the production of an electric contact member according to the present invention, a continuous plate- or rod-formed molded product can be created by extrusion and compression molding of a powder mixture consisting of fire proof metal powder and highly conductive metal powder; and the molded product can be sintered continuously under vacuum or in inert atmosphere at the melting point equal to or less than that of the highly conductive metal powder. This method allows an electric contact member to be produced at a low production cost with high productivity. Since the fire proof metal powder having the form of a flat plate tends to oriented in parallel to the direction of extrusion, it is preferred that the surface parallel to the direction of extrusion be used as a contact point face. This ensures the characteristics intended in the present invention.
The electric contact member produced can be made more compact by further continuous rolling with the result that electrode performances are made more stable. This rolling operation can be performed at the normal temperature. Cracks and other material defects can be prevented by warm rolling operation performed at the melting point equal to or less than that of the highly conductive metal. Orientation of fire proof metal powder having the form of a flat plate can be reinforced by rolling, with the result that the characteristics intended in the present invention are improved.
An electrode of a desired form can be obtained effectively in a short time by punching the produced electric contact member perpendicularly to the direction of extrusion. The particle size of the highly conductive metal powder as a material of the above-mentioned electric contact member is preferred to be 80 xcexcm or less. If the particle size of the highly conductive metal powder is greater, it will be difficult to oriented the fire proof metal powder in the process of formation of the powder mixture, and to get the characteristics intended in the present invention.
In the vacuum valve according to the present invention, the value y obtained by multiplying the rated voltage (kV) by breaking current effective value (kA) is preferred to be not more than the value obtained by the following equation (1) and not less than the value obtained by the following equation (2), based on the outer diameter x (mm) of the vacuum container:
y=11.25xxe2x88x92525xe2x80x83xe2x80x83(1) 
y=5.35xxe2x88x92242xe2x80x83xe2x80x83(2) 
In the electric contact according to the present invention, the diameter y (mm) is preferred to be not more than the value obtained by the following equation (3) and not less than the value obtained by the following equation (4), based on the value x (kVAxc3x97103) obtained by multiplying the rated voltage (kV) by breaking current effective value (kA):
y=0.15x+22xe2x80x83xe2x80x83(3) 
y=0.077x+20xe2x80x83xe2x80x83(4) 
In the vacuum valve according to the present invention, the diameter y (mm) of the vacuum container is preferred to be within the range from the value obtained by the following equation (5) or less to the value obtained by the following equation (6) or more, based on the diameter x (mm) of the electric contact:
y=1.26x+30xe2x80x83xe2x80x83(5) 
y=1.26x+10xe2x80x83xe2x80x83(6) 
The electric contact member according to the present invention has the texture wherein fire proof metal powder having the form of a flat plate is oriented parallel to the contact point face in the matrix comprising a highly conductive metal. This increases the area occupied by the fire proof metal powder and improves dielectric strength and welding resistance without reducing the breaking performance.
The production method according to the present invention allows effective mass production of the electric contact member having the above-mentioned material texture, thereby reducing the production costs.